Purpose: Postoperative acute kidney injury is common and associated with increased length of hospital stay, costs and mortality. The impact from postoperative subclinical changes in plasma concentration of creatinine (p-creatinine) on postoperative mortality has received less attention. In this study, the association between the postoperative change of p-creatinine and all-cause mortality was investigated. Methods: A single-centre register-based, retrospective study was conducted including patients ≥ 60 years undergoing open abdominal surgery from 2000 to 2013. Postoperative p-creatinine change was analysed for association with 30-day mortality following adjustment for age, gender, surgical setting and surgical procedure. Main findings A total of 3,460 patients were included in the study of whom 67.6% underwent emergency surgery. The 30-day mortality rate was 18.3%, and a given 10 μmol/L daily postoperative increase in p-creatinine was associated with an increased mortality risk with an odds ratio (OR) of 2.67 (95% CI; 2.28-3.14, P < 0.001). In patients undergoing emergency surgery, a daily 10 μmol/L increase in p-creatinine increased the risk for a fatal outcome a 2.39 OR (CI 95%; 2.05-2.78), P < 0.001). In patients undergoing elective surgery, a similar increase in p-creatinine increased risk of postoperative death with a 28.85 OR (CI 95%; 10.25-81.19). Conclusion: Even a minor postoperative p-creatinine increase following open abdominal surgery below the criteria for acute kidney injury was associated with increased 30-day mortality in patients aged 60 years or above.